How to make fog with an image plane?
In your node setup you mix Transparent with Translucent. Translucent is not a good choice, it is generally mixed with an opaque node, it is made for objects like leaves, which are opaque when light hits from the front, and gets transparent when light hits from behind, which is not how smoke works, plus if you mix it with a Transparent it might be completely transparent on one side.
You should use a mix between Transparent and Diffuse or Emission, like that: